Rubella is usually a mild childhood disease of short duration. It would be of little importance were it not for the severe birth defects which result from congenital rubella infection during the first trimester of pregnancy. Thus, the determination of the immune status of individuals is important as a means of preventing these birth defects. Serological determinations of rubella are used to determine the immune status of individuals in a given population (particularly women of child bearing age) so that those unprotected can be vaccinated. The determinations also are used to evaluate the status of pregnant women who have been exposed to rubella so that they can be counseled as to the possibility of congenital infections. Finally, the serological determination of rubella serves as a diagnostic tool for the identification of the cause of exanthematous (rash causing) diseases.
A number of methods are currently available for the detection of antibodies to rubella virus. The most common are the hemagglutination inhibition assay (HI), the serum neutralization assay, the complement fixation assay (CF), and the indirect immunofluorescent assay (IF).
Certain viruses, including rubella, having the ability to combine with and agglutinate red blood cells (hemagglutination). When antibodies to rubella combine with the virus, they prevent the agglutination of the red blood cells. Stewart, et al. New Eng. J. Med. 276:554 (1967), used these properties of the rubella virus to develop the hemagglutination inhibition assay. Since the HI assay was first described, many variations in the procedure have been presented. This has prompted the Center for Disease Control (CDC) to offer a standardized method, Standardized Rubella Hemagglutination-Inhibition Test. Immunology Series No. 3, U.S.D. H.E.W., CDC, Atlanta, Ga. 30333, Oct. 1970.
The serum neutralization assay for rubella, which was first described by Parkman et al., Proc. So. Exp. Biol. Med. 3:225 (1962), is based upon the fact that viruses which are combined with antibodies are no longer infective.
A complement fixation assay has also been described for rubella, Lennette, E. H. in Diagnostic Procedures for Viral and Rickettsial Diseases, 3rd Ed. American Public Health Association, 1-66 (1964). This is based upon the ability of the antibody-rubella complex to bind (fix) complement.
Brown et al., Science 145:943 (1964), and Schaeffer, et al., Bact. Rev. 28:402 (1964) developed an indirect immunofluorescent assay for rubella. In this assay cells which were infected with rubella were fixed on slides. The fixed cells were incubated with diluted serum samples. Rubella antibodies in the sample combine with the rubella antigens in the fixed cells. The rubella antibodies on the cells are detected with a fluorescently labeled anti-human immunoglubulin antibody.
While these tests for rubella are known, they suffer from a number of disadvantages because of their clinical complexity, expense, time consumption and quantitative reliability and for this reason it is desirable to develop a new rubella test in which rubella can be detected through fluoro immunoassay rapidly and economically with dependable quantitative results.
A number of developments have been made in recent years in the art of fluoro immunoassay where patients may be tested for a particular component of a bodily fluid by (a) binding to a support surface a known sample of the component, (b) contacting the support surface with a sample of the bodily fluid to be tested so that antibodies in the bodily fluid may be attracted to the component on the support surface, (c) contacting the surface with a fluorescent tagged second antibody to the first antibody and (d) measuring the fluorescence of the resulting surface.
A number of technologies and instruments have been developed as indicated, for instance, in the following patents by which fluoro immunoassay has achieved a new level of quantitative consistency and convenience.
U.S. Pat. No. 3,992,631--Inventor: Richard A. Harte PA1 U.S. Pat. No. 3,999,948--Inventors: Fred H. Deindoefer, et al PA1 U.S. Pat. No. 4,020,151--Inventors: Gunner Bolz, et al. PA1 U.S. Pat. No. 4,025,310--Inventors: Gunner Bolz, et al. PA1 U.S. Pat. No. 4,056,724--Inventor: Richard A. Harte
Adapting these new fluoro immunoassay techniques and devices to a rubella test is a very desirable end result but produces substantial difficulties in attempting to obtain reliable quantitative results. Apparently, there are many competing substances interfering with the normal immunoassay procedures when these procedures are applied to rubella.